The art of torque control for automatic shut-off of pneumatically powered hand held tools, is well developed and many differing designs have been proposed and utilized for attainment of the desired objective.
A type of tool having automatically operable torque shut-off means is found in U.S. Pat. No. 3,667,345, which tool incorporates a pneumatically balanced air flow control valve. Another type, using a centrifugally responsive ball valve, is disclosed in U.S. Pat No. 3,850,553. A family of tools, utilizing a push rod operable at a predetermined torque to close an air inlet valve, can be found in U.S. Pat. Nos. 2,743,635, 2,964,151, 3,059,620, 3,195,704, 3,276,525, 3,477,521 and 3,766,990. The tool of the present invention is of the last mentioned type; however, it incorporates a structural arrangement which provides advantages over known devices of the prior art.
More specifically, the device of the present invention incorporates a ball which is forced up a cam ramp when predetermined torque is realized, resulting in movement of a latch pin to cause closing of an inlet valve. In those devices using a sear, or the equivalent, a secondary camming action is required to move the sear to valve closing position. Depending upon job conditions and tool tolerances, it is possible for the sear to operate before predetermined torque is realized, thus resulting in error in torque shut-off objective. Furthermore, it is possible for the sear to cause valve closing operation when balls, or the equivalent, of an operative cam are at the crest of a cam, and if such a condition occurred, the tool could not automatically reset. Such a malfunction is avoided in the cam ramp and ball arrangement employed in the present invention, and in addition, ease of manufacture because of reduced tolerance requirements, contributes to lower manufacturing costs without sacrifice of tool operating efficiency.